In apparatuses of this kind the probe, the armature, to which is it fastened, and one or more piezoelectric crystals form an oscillating system with a resonance frequency corresponding to the frequency, at which work is desired to be carried out. In the known apparatuses the piezoelectric crystals are shaped like discs placed perpendicular to the axis of the probe and fixed with a mounting of the crystal in such a way that an electric activation brings about a mechanical change of the crystal in the axial direction of the probe. To attain a sufficient mechanical effect the crystal should have a certain area, which makes it necessary that the housing in order to hold the crystals should have a diameter of 20 nm or more. The comparatively big diameter of the cross-section of the housing makes the apparatus awkward to hold, which makes it in particular tiring to work with when very precise movements are to be carried out with the point of the probe, which is of particular importance when such apparatus are used for surgical interventions in human eyes, in which connection work is carried out with the apparatus under microscope. The comparatively big dimensions of the crystal or the crystals also contribute to making it difficult to attain very high resonancy frequencies on account of the comparatively big masses of armature and probe. It is thus difficult to attain resonance frequencies in the area of 50 to 100 kHz.